package Answer;

/**
 * @author : RobertWei
 * time: 2021/9/27    14:14
 * description:
 */

public class Demo {

    public static void main(String[] args) {

        ListNode l1 = new ListNode(1);
        l1.next = new ListNode(2);
        l1.next.next = new ListNode(3);
        l1.next.next.next = new ListNode(5);
        ListNode l2 = new ListNode(4);
        l2.next = new ListNode(4);
        l2.next.next = new ListNode(6);
        l2.next.next.next = new ListNode(7);

        ListNode merge = mergeTwoLists(l1, l2);

        while (merge != null) {
            System.out.print(merge.val + " ");
            merge=merge.next;
        }

    }

    public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode prehead = new ListNode(-1);

        ListNode prev = prehead;
        while (l1 != null && l2 != null) {
            if (l1.val <= l2.val) {
                prev.next = l1;
                l1 = l1.next;
            } else {
                prev.next = l2;
                l2 = l2.next;
            }
            prev = prev.next;
        }

        // 合并后 l1 和 l2 最多只有一个还未被合并完，我们直接将链表末尾指向未合并完的链表即可
        prev.next = l1 == null ? l2 : l1;

        return prehead.next;
    }

}

class ListNode{
    int val;
    ListNode next;

    ListNode() {
    }

    ListNode(int val) {
        this.val = val;
    }

    ListNode(int val, ListNode next) {
        this.val = val;
        this.next = next;
    }
}